The technique of warp printing is well known. There is therefore no need to describe it in detail here. This technique is reserved essentially for luxury fabrics.
For some years now these warp-printed fabrics have been obtained by means of the transfer-printing technique (see, for example, the documents FR-A-2,254,950 and 2,296,727). This technique gives excellent results, but is economically viable only for series of considerable length. Moreover, above all, if the warp to which the transfer design is applied has a defect of any kind, such as, for example, a missing thread, the fabric thus printed incorporates this defect which then becomes irreparable. As a result of this, the warp has to be inspected beforehand and the weaving checked very carefully, and this increases the cost of these fabrics in proportion.
The document CH-D-53/75 (corresponding to the document GB-A-1,528,411) suggested using this transfer-printing technique on carpets by carrying out the transfer phase on the lap of yarns intended to constitute the pile or plush loops, and then winding the lap thus printed with the transfer paper onto a beam which is subsequently placed at the head of the tufting machine. For this purpose, first of all, the design to be transferred onto the yarns must possess, in the longitudinal direction of the yarns, an elongation in relation to the design to be obtained on the carpet in order to compensate the shrinkage; the lap thus printed must thereafter be transferred onto the tufting loom, and consequently this technique has the same disadvantages as that described above.
The document BE-A-755,182 suggested the wet printing of a design on a continuously advancing lap of warp yarns on a weaving loom between the beam and the shed formation point. This technique requires complex and bulky installations which are underused because the output is limited by the production speed of the weaving loom which, as is known, is at least one thousand times lower than that of the printing installation. This is doubtless why this technique has not become more widespread.